const symid = Symbol('productno')

interface Product {
    [symid]: number,
    name: string,
    price: number,
    account: number,

    buy(): void
}

// 字面量当作类型
type A = Product['buy']
type B = Product['price']
type S = Product[typeof symid]

type PKeys = keyof Product

let pkeys: PKeys = 'account'

type AllKeys<T> = T extends any ? T : never

type Pkeys2 = AllKeys<keyof Product>

export {}
